Santanu Bera

Oxidation state of uranium: an XPS study of alkali and alkaline earth uranates

X-ray photoelectron spectroscopy (XPS) studies are performed on some mixed oxides of uranium with alkali and alkaline earth metals (Na, Li, Rb, Tl, Sr, Ba) to investigate the presence of multiple valence states of uranium in these compounds. Photoelectron peak positions, peak widths and satellite positions were measured to identify the chemical states. The analysis of the shake up satellites and the deconvolution of the principal peaks are used to quantify the chemical states. The domination of U(V) chemical state is inferred in Na2U3O9 and Sr2U3O10.

Electrochemical passivation of iron alloys and the film characterisation by XPS

The initial stages of oxide growth and composition of passive films developed electrochemically on iron alloys viz. AISI 304, 316 and incoloy 800 were studied by X-ray photoelectron spectroscopy. The results showed an enrichment of chromium in the passive films and the thickness of the films were of the same order on all the alloys. The hydroxide species were found to dominate at the oxide solution interface. The air oxidised film showed the presence of both chromium and iron in the oxidised state unlike the electrochemically developed passive film where chromium was found to be the dominant oxidised species.

Temperature programmed decomposition of uranyl nitrate hexahydrate

Abstract Temperature programmed decomposition (TPD) of uranyl nitrate hexahydrate has been studied using evolved gas analysis mass spectrometry (EGA-MS) in the temperature range 300–1400 K. Thermogravimetric (TGA) investigations were performed in the temperature range 300–1100 K. An attempt has been made to resolve the complexity of decomposition behaviour through suitable comparison of TGA and EGA-MS data. Kinetic control regimes for various decomposition stages could be deduced from EGA-MS data. The corresponding activation energies and frequency factors were also evaluated. Kinetics based on random nucleation and diffusion was found to be rate controlling. The residue left over after each decomposition stage was analysed by XRD and XPS to determine structure and composition. The ultimate product was found to be a mixture of UO 3 H 1.17 and U 3 O 8 : the former being a topotactic hydrogen spill over compound of UO 3 . Complete conversion of this residue to U 3 O 8 was noticed during ion beam exposure of the residue which was performed in the course of XPS investigations.

XPS and SIMS analysis of gold silicide grown on a bromine passivated Si(111) substrate

Abstract When a thin film of Au (∼100 nm) deposited under high vacuum conditions on a chemically prepared Br-passivated Si(111) substrate was annealed around 363°C, epitaxial layer-plus-island mode growth of gold silicide was observed along with some unreacted gold in stringy patterns. This unreacted gold was removed by etching the sample in aqua regia. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements were carried out on these samples. SIMS results reveal that the height of the islands is about 1.2 μm and the silicide/Si interface is abrupt. XPS measurements were made after sputtering the sample surface at constant intervals of time. Si 2 p , Au 4 f , C 1 s and O 1 s photoelectrons were detected. XPS spectra of Si 2 p are resolved into three peaks corresponding to bulk Si, Si in silicide and Si in oxide. The Au 4 f 7/2 peak in the silicide is shifted by 1–1.2 eV towards higher binding energy compared to metallic Au. The shift of Si 2 p towards the higher binding energy in the silicide is understood from the higher electronegativity of Au, while the shift of Au 4 f 7/2 peak towards higher binding energy is known to be due to d-electron depletion to form an sd hybrid. The XPS peak intensity profile with sputtering time indicates that the thin uniform layer (∼5.5 nm) of gold silicide is sandwiched between a thin (∼2.8 nm) SiO 2 layer and the Si(111) substrate.

Response of magnetron sputtered AlN films to controlled atmosphere annealing

The present investigation deals with the examination of the response of amorphous AlN films to post-deposition annealing environments such as high vacuum (HV) and nitrogen atmosphere (NA). The c/a ratio values from GIXRD for both cases are around 1.602. The XPS profile of NA-AlN shows a deficiency of nitrogen on the surface, whereas the oxygen impurity level is negligible in the case of NA compared with HV. The PL spectra substantiate the nitrogen vacancies in NA-AlN. The amorphous AlN exhibits a nanoindentation hardness of 18 GPa.

Ion-beam induced transformations in nanoscale multilayers: Evolution of clusters with preferred length scales

Ion-irradiation-induced modifications of a periodic Pt∕C multilayer system containing a small amount of Fe have been analyzed by transmission electron microscopy and grazing incidence x-ray diffraction (GIXRD) studies. The multilayer stack with 16 Pt∕C layer pairs (period of 4.23nm) was fabricated on a glass substrate. A 2MeV Au2+ ion beam was rastered on the sample to obtain uniformly irradiated strips with fluences from 1×1014to1×1015ions∕cm2. Ion irradiation has been found to cause preferential migration of Fe towards Pt layers [Bera et al., Nucl. Instrum. Methods Phys. Res. B 212, 530 (2003)]. Cross-sectional transmission electron microscopy (XTEM) shows considerable atomic redistribution for irradiation at the highest ion fluence (1×1015ions∕cm2). This structure is composed of small clusters. Phase separation and cluster formation processes are discussed. Periodic multilayers have periodicity only in the direction normal to the multilayer surface. However, Fourier transform (FT) of the XTEM images of...

Analysis on Binding Energy and Auger Parameter for Estimating Size and Stoichiometry of ZnO Nanorods

ZnO nanorods prepared through chemical vapor deposition technique are characterized by microscopic and X-ray photoelectron spectroscopy (XPS) techniques to correlate the effects of size on the binding energy of Zn 2p3/2 photoelectrons. A positive shift in Zn 2p3/2-binding energy as compared to that in bulk ZnO is assumed to be the effect of size of ZnO tips. The shift in binding energy has been explained in terms of relaxation energy in the photoemission process. Simultaneously, Auger parameter of the nanorods is evaluated for stoichiometric composition. The extra peak in O1s spectrum of nanorods is explained as adsorbed O-bearing species or surface contaminants.

Temperature programmed decomposition of thorium nitrate pentahydrate

Abstract Temperature programmed decomposition (TPD) of thorium nitrate pentahydrate has been studied using evolved gas analysis–mass spectrometry (EGA-MS) in the temperature range 300–1200 K. A thermogravimetric (TGA) investigation was also carried out in the same temperature range. Complexity of the TGA decomposition profile was resolved through use of EGA-MS data. The activation energies and pre-exponential factors were determined for various gas release stages from the fractional extent of decomposition plots. Residues left over after each decomposition stage were analysed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD investigations revealed formation of a nanocrystalline thoria intermediate product, ultimately agglomerating to a microcrystalline phase. The XPS investigations indicated systematic alteration in the chemical environment around the thorium atom while the Th4+ oxidation state remained unchanged. This was further corroborated from the analysis of shake-up satellites of Th (4f5/2) spectra. The O/Th ratios for various intermediate products were also determined.

Deposition and characterization of laser ablated poly(p-phenylene sulfide) thin films

Abstract Thin films of poly(p-phenylene sulfide) [PPS], were deposited by pulsed laser deposition with a doubled Nd:YAG laser (λ=532 nm) on Si (100) and quartz substrates at temperatures above and below the glass transition temperature (Tg) of the polymer. SEM micrographs of the films showed a decrease of particulate size with increasing substrate temperature. An absorption band edge at 3.4 eV in the UV–VIS spectrum of the deposited film indicated that they were polymeric as well as insulating. FTIR spectra of films deposited at various substrate temperatures mimicked all characteristic vibrational frequencies observed in pristine bulk samples. Low-angle X-ray diffraction patterns and FTIR spectral analysis of the deposited PPS films confirmed that the crystallinity was enhanced when the substrate temperature during deposition exceeded Tg. X-ray photoelectron spectroscopic (XPS) investigations of the C1s spectra of the as-deposited film on Si (100) revealed oxidation of the surface with the formation of sulfone, sulfoxide, C–O and CO. Ar+ ion sputtering with a 4 keV beam at 1 μA beam current removed ∼2 nm of the surface film and completely eliminated the sulfone peak from the XPS spectra, retaining a very negligible oxide component.

Microstructural evolution, atomic migration, and FePt nanoparticle formation in ion-irradiated Pt(Fe)/C(Fe) multilayers

Ion-irradiation-induced microstructural modifications, atomic migration, and nanoparticle formation in nanoscale periodic Pt/C multilayer systems containing about 15 at. % Fe have been analyzed by x-ray reflectivity, x-ray standing wave (XSW), transmission electron microscopy, and grazing incidence x-ray diffraction (GIXRD) studies. The multilayer stack with 15 Pt(Fe)/C(Fe) layer pairs (period 4.2 nm) was irradiated with a 2 MeV Au2+ ion beam, which was rastered on the sample to obtain uniformly irradiated strips with fluences (ϕ) from 1×1014 to 1×1015 ions/cm2. Up to a certain threshold ion fluence (ϕt) we have observed mixing between Pt and C atoms. At higher fluences (ϕ>ϕt) demixing effect is pronounced. This phenomenon has been explained in terms of two competitive processes including ballistic and chemically guided atomic movements. As revealed by XSW measurements, ion irradiation causes preferential migration of Fe toward Pt layers from C layers. Consequently Fe concentration in the Pt layers increa...